There has been much talk about the wonderful sound of magnetic tape. = Many=20 have taken the DSP software approach to tease out what actually happens = when=20 tape is used, with dubious results in my opinion. I have chosen instead = to take=20 the fully analog road and develop a circuit that provides the sonic = effect of=20 actual tape saturation.=20
This is not just a frequency dependant filter, as some popular = product that=20 claims to capture the sound of tape saturation. This circuit actually = duplicates=20 the effect of what tape does to the transfer curve, and subsequent = effects of=20 pre-emphasis and de-emphasis of tape recording and playback electronics.
I carefully set up several listening tests to determine the correct = values=20 that got closest to that elusive tape sound. There is no mumbo-jumbo = here, just=20 the most elegant implementation.
Be aware of the fact that there is far more to the sonics of magnetic = tape=20 than just some simple little circuit pretending to sound EXACTLY like = tape. This=20 has not yet been accomplished, anywhere! Don't be fooled by cheap = promises.
However, if you want a circuit that will give you a very convincing = replica=20 of that elusive effect, this may be for you.=20
This circuit is a waveform compressor that compresses more at higher=20 frequencies. It consists of a 70 microsecond (2.25 KHz) pre-emphasis, = followed=20 by a diode type waveform compressor, followed by a 70 microsecond = de-emphasis.
This compressor has an unusually good sound considering the lack of = time=20 constants. Distortion and "pumping" effects are both virtually = inaudible.
This circuit was designed to simulate the effects of analog tape = compression.=20 It will be useful with digital tape recording equipment if a more = "analog" sound=20 is desired.
Click = here for=20 the schematic.
Notes for this circuit:
1. Power supply is a split supply of +/- 15 volts.
2. Any decent quality op-amps can be used.
3. If equipment feeding or being fed by this circuit has any = extraneous DC=20 voltages, you will need to add blocking capacitors.
4. UPDATES AND REVISIONS:
There have been some changes that were added to the circuit.
C1 was added to prevent any dc from entering the input. R5 was = added in=20 conjunction with the gain stage to provide some make up gain after the = diode=20 block. This also provides a way to get various levels of saturation = while having=20 a constantly adjustable output level. C4 was added as an output = blocking=20 capacitor. It is generally not needed.
Furthermore, you may be inclined to experiment with the value R4 that = feeds=20 the diode block. Previous experiments have shown different waveform = compression=20 charicteristics with different resistor values. I chose the 10k value = because it=20 sounded best to my ear.
PARTS LIST
=0A= R1..........100K AUDIO TAPER=0A= R2..........1.5K=0A= R3..........22K=0A= R4..........10K=0A= R5..........100K AUDIO TAPER=0A= R6..........1K=0A= R7..........10K=0A= R8..........22K=0A= R9..........1.5K=0A= R10.........150 OHMS=0A= C1..........0.1UF=0A= C2..........0.003UF=0A= C3..........0.003UF=0A= C4..........10.0UF NOT NEEDED IN MOST APPLICATIONS=0A=